Well, you're giving up a lot of runs/sb's for Vlad, but he is Vlad. He's one of the top players in fantasy, but so is Ichiro. I'd say it's a fair trade. You're not getting screwed, but you do have to consider if it's worth it to you.
One thing I remember reading about Ichiro is that because he walks so few times and gets so many hits and ab's, his high average holds a greater weight in fantasy than a typical player. He can really help carry the batting average category. He'll also get tons of runs, of course. Kenny Lofton seems to be holding up well this year, too. Steals are more valuable than home runs in most fantasy leagues, and you're definitely hurting yourself in that category. The guy you give Ichiro and Lofton too will most likely win SB's, if he's in contention now.
Tough call, but I don't think I'd do it. In head to head, I would because it's all just total points, but when SB's and runs are two separate categories, I think you're giving up too much. Unless you're really behind in RBI and HR, it's too much. Delgado and Ichiro sounds perfect, as you get to keep one of your SB guys and he gets some power back. He's still getting a lot of value for Vlad, so it's fair. I'd understand if he doesn't go for it, though! Guerrero is definitely someone that I would be reluctant to trade away.